The present invention relates to a drive system which is comprised of a waste heat recovering device including a displacement-type expander and a power transmission system for transmitting the output of the expander to a driven portion.
Japanese Patent Publication No. 7-35846 discloses an exhaust energy recovery apparatus which is comprised of a turbine driven by exhaust gas of an internal combustion engine, a power generator driven by the turbine, a motor driven by power generated by the power generator, and a planetary gear mechanism for combining the shaft output of the motor with the shaft output of the internal combustion engine. According to the exhaust energy recovery apparatus, it is possible to recover a part of energy of exhaust gas that has been conventionally discarded without being effectively used so as to assist the shaft output of the internal combustion engine, thereby contributing to a reduction in consumption of fuel.
It should be noted here that the above conventional device suffers from a problem that kinetic energy of exhaust gas is used to drive the turbine and hence, thermal energy of high-temperature exhaust gas cannot be effectively used, resulting in low efficiency of recovering energy. Thus, it has been considered that exhaust energy is recovered by a Rankine cycle comprised of an evaporator for heating water by using thermal energy of exhaust gas to generate high-pressure vapor, an expander for conversing high-pressure vapor, which is supplied from the evaporator, to shaft output with constant torque, a condenser for liquefying low-pressure vapor discharged from the expander, and a feed pump for supplying water liquefied by the condenser to the evaporator. In this case, a displacement-type expander is adopted, so that it is possible to obtain high efficiency in a wide rotational speed region of the expander, thereby more effectively recovering energy of exhaust gas.
When a displacement-type expander is adopted in an waste heat recovering device of a Rankine cycle type, the shaft output of the expander has time delay relative to the shaft output of the internal combustion engine. In addition, the expander is characterized by shaft output with constant torque and a rotational speed determined by shaft output of the internal combustion engine. Therefore, in order to effectively use the shaft output of the expander, it is necessary to provide a special power transmission system, which is suitable for the above described characteristics, between the expander and a driven portion driven by the expander.
The present invention is achieved in view of the above described circumstances and an object thereof is to effectively drive a driven portion by using an output of an expander of a waste heat recovering device forming a Rankine cycle.
In order to attain the above object, according to the present invention, there is provided a drive system which comprises a waste heat recovering device forming a Rankine cycle by an evaporator for heating a working medium with a waste heat of a prime mover to generate a high-pressure vapor, a displacement-type expander for converting high-pressure vapor generated by the evaporator to output with constant torque, a condenser for liquefying low-pressure vapor discharged from the expander, and a pump for supplying a working medium liquefied by the condenser to the evaporator; and a power transmission system for transmitting the output of the expander to a driven portion, the power transmission system driving the driven portion according to the output characteristics of the expander.
With the above arrangement, regarding the expander of the Rankine cycle using a waste heat of the prime mover as a heat source, the output characteristics include time delay relative to the output of the prime mover, and changes in rotational speed with constant torque relative to changes in output of the prime mover. The power transmission system disposed between the expander and the driven portion drives the driven portion according to the above output characteristics of the expander, so that the output of the expander can be effectively used.
Further, in addition to the above arrangement, there is provided a drive system, wherein the power transmission system drives the driven portion within a range of the output characteristics of the expander.
With the above arrangement, since the power transmission system drives the driven portion within a range of the output characteristics of the expander, it is possible to prevent the expander from operating beyond the range of the output characteristics and reducing efficiency.
Moreover, in addition to the above arrangement, there is provided a drive system, wherein the power transmission system can distribute the output of the expander to a plurality of driven portions in an arbitrary ratio.
With the above arrangement, since the power transmission system distributes the output of the expander to a plurality of driven portions in an arbitrary ratio, the output of the expander can be applied for a variety of uses to enhance general-purpose utility.
Moreover, in addition to the above arrangement, there is provided a drive system, wherein the power transmission system comprises at least a planetary gear mechanism.
With the above arrangement, since the power transmission system comprises the planetary gear mechanism, the output of the expander can be properly distributed to a plurality of driven portions.
Besides, an internal combustion engine 1 of an embodiment corresponds to the prime mover of the present invention, and a power generator/motor 124 and a transmission 143 correspond to the driven portions of the present invention.